1. Field of the Invention
The invention relates to a method and apparatus for the leveling of a template at an offshore location and on an ocean or sea bed.
2. Description of the Prior Art
The demand for new sources of oil and gas in recent years has brought a dramatic increase in the amount of well drilling and completion on the ocean floor. Such wells are drilled at depths ranging from fifty to several thousand feet and a variety of techniques are employed to effect first the drilling of the well and then the installation of completion and production equipment to remove the hydrocarbons. Because of the substantial cost of installing a platform, particularly at increased water depths, drilling and completion operations are commonly performed from a drilling or other barge and at any one drilling site, a number of wells are concurrently drilled and incrementally completed. Since it may require from twelve to eighteen months to build and assemble in place an offshore platform, it is necessary, once the wells have been drilled and are capable of production, to provide means for capping each well during the intervening period, and also for connecting the well casings to the completion and production equipment once the drilling platform is ready to be installed. For these purposes, a template is utilized which comprises a relatively massive structure formed of welded tubing and involving a number of flotation tanks so that the bouyancy of the template can be controlled by alternately introducing water or air within the hollow interior of the template frame structure for the purpose of landing the template upon the ocean floor. Alternatively, the template may be installed on a plurality of fixing piles sunk in the ocean floor and the well drilling, completion or production equipment mounted on the template. In either event, it is essential that the template be positioned in a precisely level or horizontal position so that cable guide bushings and other sleeves provided on the template will permit down hole drilling, completion or production equipment to pass therethrough and into accurate alignment with the well bores.
It is difficult to drill and mount in cement in the ocean floor at least three fixing piles in a precisely vertical position. Instead, the piles are mounted in drilled bores and cemented therein in as nearly an upright position as is possible, and then cooperating sleeves rigidly secured to the template in the same horizontal spacing as the fixing piles, which sleeves are several inches larger in internal diameter than the fixing piles, are slipped freely over such piles regardless of any minor misalignments in the vertical inclination of the fixing piles.
It previously was necessary to secure each of the encircling sleeves to the fixing piles by cement, with the template disposed in exactly a horizontal position, and, considering the fact that the size of the template may range up to one hundred feet per side and the mass of the template may be on the order of one hundred tons, this leveling operation has been a matter of some difficulty to accomplish by divers and has required an inordinate amount of diving time in order to achieve the level positioning of the template, and then the cementing of the template to the fixing piles in a precisely level position. Moreover, when it became desirable to abandon the particular well site, the recovery of the template was very difficult, because it could only be accomplished by underwater cutting operations since the mounting sleeves were rigidly attached to the fixing piles by cement or grout. Also, due to the low shear strength of the hardened grout, the sleeves were required to be very long which interfered with the jacket placement over the template.
Further details concerning prior uses and mountings of templates may be found in U.S. Pat. Nos. 3,612,177 and 3,618,661.
There is an apparent need, therefore, for an improved method and apparatus for effecting the leveling and securement of a template to its fixing piles on the ocean bed involving a minimum amount of diver involvement in the positioning operation.